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  Method and devices for cardiac radiofrequency catheter ablationRelated Patent Categories: Surgery, Instruments, Electrical ApplicationThe Patent Description & Claims data below is from USPTO Patent Application 20070049915. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] The application claims the benefit of Provisional Patent Application entitled "Quantification of Local Convectional Cooling During Cardiac Radiofrequency Catheter Ablation", by Haemmerich and Saul, Ser. No. 60/711,742 filed on Aug. 26, 2005, and hereby incorporated by reference as if rewritten in full. BACKGROUND OF THE INVENTION [0002] Radiofrequency (RF) ablation is a medical procedure which can be used to treat some types of rapid heart beating including conditions such as supraventricular tachyarrhythmias. Ablation can be used to treat a wide variety of tachycardias, which can involve heart tissues in the upper chambers (atria), also called supraventricular, or the lower chambers (ventricles), called ventricular tachycardias (SVT or VT). In some cases, a small number of cells (a "focus") start firing rapidly and ablation can eliminate the focus. In other types of tachycardia, an electrical circuit exists within which the electrical signal travels more or less in a circle ("reentry"). Many cases of SVT and VT are due to reentry. A special type of SVT, called atrial fibrillation, is characterized by extremely fast impulses in the atrium (up to 600/min), for which ablation can be used either to decrease the number of impulses getting to the ventricles or in some cases to locate and ablate the area(s) from which the fibrillation starts. (Circulation. 2002;106:e203.) [0003] An example of an ablation procedure is as follows: A physician guides a catheter with an electrode at its tip to the area of heart muscle where there's an accessory (extra) pathway. The catheter is guided with real-time, moving X-rays (fluoroscopy) displayed on a video screen. The procedure helps the doctor place the catheter at the exact site inside the heart where cells give off the electrical signals that stimulate the abnormal heart rhythm. Then a mild, radiofrequency energy (similar to microwave heat) is transmitted to the pathway. This destroys carefully selected heart muscle cells in a very small area (about 1/5 of an inch). That stops the area from conducting the extra impulses that caused the rapid heartbeats. [0004] Radiofrequency current can be alternating current that is delivered at cycle lengths of 300 to 750 kHz when used for catheter ablation. It causes resistive heating of the tissue in contact with the electrode. Because the degree of tissue heating is inversely proportional to the radius to the fourth power, the lesions created by radiofrequency energy are small. Typical ablation catheters, which are 2.2 mm in diameter (7 French) and have a distal electrode 4 mm long, create lesions approximately 5 to 6 mm in diameter and 2 to 3 mm deep. Larger lesions are possible with larger electrodes or saline-irrigated ablation catheters. Although electrical injury may be a contributing factor, the primary mechanism of tissue destruction by radiofrequency current is thermal injury. Irreversible tissue destruction can require a tissue temperature of approximately 50.degree. C. In most ablation procedures, the power output of the radiofrequency generator is adjusted manually or automatically to achieve a temperature of 60 to 75.degree. C. at the electrode-tissue interface. If the temperature at the electrode-tissue interface reaches about 100.degree. C., coagulated plasma and desiccated tissue may form on the electrode, preventing effective delivery of the current, predisposing the patient to thromboembolic complications, and necessitating the removal of the catheter so that the coagulated material can be wiped off the electrode. The acute lesion created by radiofrequency can consist of a central zone of coagulation necrosis surrounded by a zone of hemorrhage and inflammation. Chronic lesions are often characterized by coagulation necrosis and have a discrete border. Changes that occur in the border zone can explain why arrhythmias may recur several days to several weeks after apparently successful ablation. The arrhythmia may recur if the target tissue is in the zone bordering a lesion instead of in the central area of necrosis and if the inflammation resolves without residual necrosis. Conversely, the site of origin of an arrhythmia that has not been successfully ablated may later become permanently nonfunctional if it is within the border zone of a lesion and if microvascular injury and inflammation within this zone result in progressive necrosis. (New England J of Medicine, Volume 340:534-544, Feb. 18, 1999). BRIEF SUMMARY OF THE INVENTION [0005] Embodiments of the invention comprise methods for computing convection cooling parameters associated with the site for the application of RF ablation. Additional embodiments of the invention comprise devices for the control of cardiac RF ablation. Further embodiments of the invention comprise computer readable medium capable of execution in a computer or other processing unit whereby an ablation lesion size is predicted based upon the input of certain parameters or measurements. Parameters can be such things as temperature measured at the electrode tip of a catheter while the catheter is energized with RF energy. Other parameters can be temperature measured at the electrode tip of a catheter for a fixed time period after the application of RF energy to the catheter. Parameters can also be those known to one of ordinary skill in the art that characterize the RF energy applied to the tip, including frequency, pulse shape, pulse duration, magnitude, and temperature of the tip. BRIEF DESCRIPTION OF THE DRAWINGS [0006] FIG. 1. Heat transfer mechanisms during RF ablation. [0007] FIG. 2. Two parameters (dTmax and slope) are derived from application of a brief RF pulse. [0008] FIG. 3. Schematics of Tissue-Phantom Setup. [0009] FIG. 4. Schematics of flow rig. [0010] FIG. 5. Schematic of electrical system setup. The laptop controls the switch, which relays RF current to either the saline beaker, or the ablation catheter. [0011] FIG. 6. Measurement of lesion dimensions. [0012] FIG. 7. Lesion depth (A) and width (B) at different flow rates, with linear approximation. [0013] FIG. 8a. Lesion depth (A) and width (B) versus maximum temperature change (dTmax), with linear approximation. [0014] FIG. 8b. Lesion depth (A) and width (B) versus slope (slope), with linear approximation. [0015] FIG. 9. The measured parameters (dTmax or slope) can be used to estimate convective cooling allowing use of computer models for accurate lesion estimation. [0016] Table 1. Temperature, Power, Impedance, and lesion dimensions at different flow rates. [0017] Table 2. Absolute (mm) and relative error (%) of lesion width and depth predicted by parameters dTmax, and slope using linear regression equations. [0018] Table 3. t-test: comparison of lesion dimensions at different flow rates. DETAILED DESCRIPTION OF THE INVENTION [0019] Cardiac radiofrequency (RF) catheter ablation has become the treatment of choice for a wide array of both supraventricular and ventricular arrhythmia. The dimensions of the lesion created during RF ablation depend on several factors such as catheter geometry, catheter-endocardial contact, and blood flow. Several studies examined the dependence of lesion size on blood flow [1-4]. Convective cooling by the blood carries away heat from the catheter tip and endocardium, enabling deposition of more RF energy deeper into the tissue. When RF power is not limited, higher blood flow can result in wider and deeper RF lesions. These results have been shown in ex vivo experiments [1, 3] and computer models [4, 5]. Similarly, in vivo experiments in a porcine animal model have shown that ablation site within the heart affects lesion size. Mukherjee, et al., classified different ablation sites in the endocardium according to flow conditions (low/medium/high), and found significant differences in lesion size depending on ablation site [2]. Continue reading... Full patent description for Method and devices for cardiac radiofrequency catheter ablation Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and devices for cardiac radiofrequency catheter ablation patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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